(1) Field of the Invention
The present invention generally relates to an electron-beam exposure method and system, and more particularly to an electron-beam exposure method and system which can be easily used width an optical exposure system in a semiconductor device production process.
(2) Description of the Related Art
In general, in order to perform a exposure process on a plurality of layer in a wafer, the wafer processed by an electron-beam exposure system has marks which are readable by the electron-exposure system. The marks are formed at four corner portions of each of areas for IC chips on the wafer. In the electron-beam exposure system, the marks are used to decide a position at which the electron-beam exposure process is to be performed.
In the electron-beam exposure system, an electron-beam scans the marks so as to cross on the marks, and reflected electrons are then detected so that the marks are detected. On the other hand, in an optical exposure system, marks on a wafer are detected by measurement of interference of light and/or the intensity of reflected light.
Thus, to obtain the clear reflected electrons, the marks which are detectable in the electron-beam exposure system must be deeper than the marks which are detectable in the optical exposure system. That is, the marks which are detectable in the optical exposure system may not be used for the electron-beam exposure system.
Meanwhile, in recent years, due to increasing of the integration degree of an IC, exposure patterns are thinned. As a result, in a case where the exposure process is carried out in a plurality of layers of a wafer, it may be necessary to use the electron-beam exposure system for a layer instead of the optical exposure system used for other layers. Thus, there are cases where the system for performing the exposure process is switched from the optical exposure system to the electron-beam exposure system and vice versa, based on layers to be processed in the wafer.
In a case where the optical exposure process and the electron-beam exposure process are carried out for a single wafer, as shown in FIG. 1, a wafer 10 must be provided with two types of marks 11 and 12. The first type of mark 11 is detectable in the optical exposure system, and the second type of mark 12 is detectable in the electron-beam exposure system. However, the first type of mark 11 and the second type of mark 12 must be formed on the wafer 10 in different processes. Thus, the manufacturing cost of the wafer 10 is increased.
That is, the conventional electron-beam exposure o process and system are not easily used with the optical exposure process for a single wafer.